The present invention relates to an electron beam writing technique for use in processing and writing of a Large Scale Integration circuit.
To cope with microfabrication of a Large Scale Integration circuit, a lithography technique has been developed continuously. In the extension of prior art optical lithography, shortage of resolution and difficulty in reticle manufacturing have been the problems. In electron beam lithography having an established reputation for resolution, increasing throughput has been tackled.
As a method for increasing throughput, as described in Japanese Patent Application Laid-Open No. 9-245708, there is a method for writing while scanning a micro unit area with multi point beams. In the method, an electron beam irradiated from one electron source is divided into multi electron beams by an aperture array to form an intermediate image by a lens array and a deflector array from the beams, and then, after on/off controlling each of the beams by a blanking array, the intermediate image is projected onto a wafer by projection optics including a deflector for writing. This method can correct field curvature and distortion caused in the projection optics by the lens array and the deflector array. The projection optics can be easily designed to realize high resolution and high throughput.
FIG. 1 shows the movement of an electron beam 102 on a wafer by the method. Each of multi electron beams is scanned at high speed in the range of a unit writing area 101 (the maximum writing area in which each of the multi electron beams can be deflection scanned successively). At this time, the beam is turned on/off at the position of each pixel 104 (49 pixels in FIG. 1) to form a pattern. The stitch of the unit writing areas 101 of the multi electron beams (64 multi beams in FIG. 1) is called a multi beam area 103. In this method, scanning 105 of the unit writing area 101 is basically performed to all the multi beams by the same deflector. Roughly, the unit writing areas 101 of the same size are formed. A plurality of the multi beam areas 103 are stitched horizontally to form a main field 106. The main fields are stitched vertically to form a stripe 107. The stripes are arrayed for write the entire surface of the wafer.
In this method, variations produced in the relative positions between the multi electron beams and the scanning distances and the electron currents in the unit areas, and deformation of the unit writing area cause deterioration of positioning accuracy and sizing accuracy in all the areas in the surface of the wafer. These variations are caused by a manufacture error of an electron optical element, an adjustment error of a driving circuit or non-uniformity of an electron gun.
An idea for improving part of the influence is shown in Japanese Patent Application Laid-Open No. 10-64812. As shown in FIG. 2, when a writing pattern 204 written with an electron beam 201 is across a unit writing area 203, an extended unit writing area 202 is set to write the pattern twice in an overlapped part to prevent the pattern from being cut. It is impossible to improve the positioning accuracy and the sizing accuracy in the entire writing area.